String Slicing

String slicing allows you to extract a portion of a string.

It takes two parameters: the starting index and the length (optional). It returns a new string containing the extracted portion.

Let's perform such operations on the string "computer". Its structure is the following:

Single argument slicing

Skip the first couple of symbols

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(3); return 0; }

Output:

puter

In this example, str.substr(3) skips the first 3 symbols of the string - 'c', 'o', and 'm'.

The remaining part of the string (starting from the 3rd index - 'p') is extracted - puter.

Selecting the last couple of symbols

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(str.length() - 3); return 0; }

Output:

ter

In this example, str.substr(str.length() - 3) extracts only the last 3 symbols of the string - 't', 'e', and 'r'.

The way it works is simply skipping the first 5 symbols.

str.length() is the count of the string symbols - 8 in this case.

The code is absolutely the same as this:

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(5); return 0; }

Output:

ter

Two arguments slicing

Allows selecting symbols in a certain range.

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(3, 2); return 0; }

Output:

pu

In this example, str.substr(3, 2) skips the first 3 symbols of the string - 'c', 'o', and 'm'.

Afterwards, it takes 2 symbols - p and u.

This way we can also skip the first and last characters like this:

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(1, str.length() - 2); return 0; }

Output:

ompute

In this example, 1 skips the first character - c.

str.length() - 2 is the same as 8 - 2 which is 6. So it takes the rest of the string until 6 symbols are taken.

Invalid cases

An invalid case results in an exception.

It uses indexes outside of the string bounds.

Such an example is using negative starting index:

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(-2); return 0; }

Another example which throws an exception is using a positive index that's outside of the string bounds.

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(22); return 0; }

Negative Second Argument

Specifying negative second argument results in the same string as specifying only a single argument:

#include <iostream> #include <string> using namespace std; int main() { string str = "computer"; cout << str.substr(2, -1) << endl; cout << str.substr(2); return 0; }

Output:

mputer mputer